This invention relates to shielding, or partially shielding, a valve element, such as a valve gate. For example, a valve gate used to close a valve passage and isolate chambers in an ion implantation system may be shielded from ions or other harmful environmental conditions while the valve is open.
Valves are used in various applications to isolate two regions from each other and/or control the flow of substances, and in some cases harmful or corrosive substances, from one point to another. In some cases, the substances can cause damage to various valve elements, such as a valve gate or other sealing elements in the valve. For example, some ion implantation systems used to introduce conductivity-altering impurities into semiconductor wafers include a vacuum valve to isolate a source chamber, or a portion of the source chamber, from other parts of the implantation system. This isolation facilitates changing of an ion source, since other portions of the implantation system can be maintained under high vacuum while only a very small portion of the ion source chamber is vented to atmospheric pressure to change the ion source. Once the ion source has been changed, the isolation valve can be reopened to reestablish a high vacuum in the ion source chamber and to allow ions from the source to be transported along the beamline of the implantation system. However, when the valve is open, heat caused by production of the ions and/or ion deposits on the various valve elements, such as the valve gate and/or valve seat, can cause damage to the point that the valve cannot properly seal the ion source chamber from other portions of the implantation system.
The invention provides a method and apparatus for shielding valve elements from exposure to harmful substances or other environmental conditions while the valve is open. For example, in one aspect of the invention, when a valve gate is retracted from a closed position to a retracted position, a shutter can be closed to shield the valve gate from potentially harmful environmental conditions, such as heat and/or ions. That is, as the valve gate is moved from a closed position to a retracted position, the valve gate moves from within an exposed region that communicates with a valve passage to a shielded region that does not communicate with the valve passage, or has a more limited communication with the valve passage than the exposed region. While in the shielded region, the valve gate is shielded from environmental conditions within the valve passage.
The invention also provides a valve having a valve body and a valve passage formed in the valve body that allows fluid communication between a first side and a second side of the valve body. A valve gate seat is associated with the valve body, so that when a valve gate is moved into a closed position, the valve gate contacts the valve gate seat and prevents fluid communication through the valve passage. The valve gate can be retracted along a travel passage to a retracted position to allow fluid communication through the valve passage. When the valve gate is moved to the retracted position, a shutter may close the gate passage to impede communication between the valve passage and the valve gate through the travel passage. For example, the valve gate may be retracted into a housing and the shutter may close an opening in the housing so that the valve gate is protected from harmful environmental conditions present in the valve passage. The valve gate need not be completely protected from the environmental conditions in the valve passage, but may be partially protected from the environmental conditions.
In one aspect of the invention, the shutter may include a shutter door that is rotatably attached to a housing so that the shutter door may move to open and close an opening in the housing. Thus, when a valve gate is retracted within the housing, the shutter door may rotate to close the opening in the housing. When the valve gate is to be extended out of the housing through the opening, the shutter door may open and allow passage of the valve gate. The shutter may include a spring or other actuator that biases the shutter door toward a closed position. Alternately, the shutter may include an actuator that drives the shutter door to open and close at desired times. The shutter door may also open and/or close in response to the valve gate moving between the retracted position and the closed position.
These and other aspects of the invention will be apparent and/or obvious from the following description.